1. Field of the Invention
The present invention relates to an occupant sensing system, which senses an occupant state on a seat and transmits the sensed result to an occupant protective apparatus (e.g., an air bag apparatus or a seat belt pretensioner), and also relates to an adjustment method thereof.
2. Description of Related Art
An occupant sensing system is used to determine an occupant state on a seat of a vehicle (see, for example, Japanese Unexamined Patent publication No. 2003-14528, which corresponds to U.S. Pat. No. 6,759,604). The occupant sensing system includes load sensors and an occupant sensing electronic control unit (ECU). The occupant sensing ECU stores an empty-state 0 (zero) point load value and one or more occupant determination threshold values. The empty-state 0 point load value indicates the load on the empty seat, on which no occupant is present. Each occupant determination threshold value is a threshold value, which is used to determine a type of an occupant on the seat. There is provided at least one occupant determination threshold value depending on the type(s) of occupant(s) or occupant state(s) to be determined.
For example, when three types of occupant states, i.e., an empty, a child and an adult need to be determined, there are provided two threshold values, i.e., an empty/child occupant determination threshold value and a child/adult occupant determination threshold value. In the case where the seat is empty, it is possible to determine whether the seat is empty by comparing the sensed data value of the load sensors with the empty/child occupant determination threshold value. When it is determined that the seat is empty, deployment of an air bag apparatus provided to the seat is prohibited or is disabled. In contrast, when it is determined that the seat is not empty, it is then determined whether the occupant on the seat is a child or an adult by comparing the sensed data value of the load sensors with the child/adult occupant determination threshold value. When it is determined that the occupant on the seat is the child, the deployment of the air bag apparatus provided to the seat is prohibited. However, when it is determined the occupant on the seat is the adult, the deployment of the air bag apparatus is enabled. As described above, the occupant determination threshold values are used to determine whether the occupant protective apparatus should be actuated.
However, the empty-state 0 point load value could vary from one seat to another seat due to, for example, a difference in a type of the seat, a difference in the amount of distortion encountered at the time of installing the load sensors to the seat or at the time of installing the seat having the load sensors to a vehicle body. Thus, adjustment of the occupant determination threshold values needs to be performed after the installation to improve the accuracy of the occupant determination performance.
However, in the previously proposed case, the occupant determination threshold values are adjusted by actually placing an intermediate reference weight, which is intermediate between a weight of the child and a weight of the adult, on the seat. Thus, depending on the way of placing the intermediate reference weight on the seat (e.g., depending on vibrations of the seat at the time of placing the intermediate reference weight on the seat) or an error in the intermediate reference weight, the applied load to the load sensors may be varied to decrease the occupant determination accuracy. Furthermore, when variations in the sensed data values of the load sensors need to be reduced to address the above disadvantage, the costs of the occupant sensing system are disadvantageously increased.